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Evaluation of convective heat transfer coefficient in crop drying under open sun drying conditions
07 Alternative energy sources (solar energy) 02/01004 Diffuse solar irradiation model evaluation in the North Mediterranean Belt area De Miguel, A. cr rrl. Solrrr Energy, 2001, 70, (2) 143-153. The performance of daily and hourly diffuse horizontal solar irradiation models and correlations is examined using an assembled data set of multivariate meteorological time series from countries in the North Mediterranean Belt area. The correlations reviewed use only daily global, hourly global or daily diffuse irradiation as input, for the daily or hourly time scale. The best overall performance was presented by the Frutos correlation for the estimation of the daily diffuse radiation by an adapted version of the Liu and Jordan correlation for the mean daily diffuse radiation profile, and by the Hollands and Crha model for estimation of hourly diffuse values from the corresponding global values. The results show that best correlation for each site varies. Two empirical piecewise correlation were also developed by the authors with the help of the data bank available, yielding models that showed even better fits to the data. The results show some seasonal and location dependence.
02/01009 Integration of a desiccant unit in crops solar drying installation: optimization by numerical simulation Hodali, R. and Bougard, J. Energy Conversion and Manugemenf, 2001, 42, (13) 154331558. An adsorption unit of silica gel is designed and integrated in a crops solar drying installation. The installation consists of a direct flat plate forced convective solar dryer connected with a similar solar collector. The daily sorption cycle of the desiccant unit is first investigated and a suitable coupling of the collector, the dryer and the adsorption unit has been selected. The coupling is numerically simulated and applied to the drying of apricots and Morocco under real climatic conditions. The mathematical model assumes non-isotermal processes and employs the basic balances of heat and mass transfer. The developed non-linear partial differential equations were solved by finite difference methods and the physical and operational parameters of the installation were numerically optimized. The integration of the adsorption unit allowed improving the quality of the dried product and permitted a cyclic operation of drying over two days by reducing the drying period from 52 to 44 h.
02/01005 Efficient orientation impacts of box-type solar cooker on the cooker performance Algifri, A.H. and Al-Towaie, H.A. Solar Energr, 2001, 70, (2) 165-170. The addition of a plane reflector to a box-type solar cooker increases the obtained cooker temperature and this depends upon the efficient orientation of the cooker. In order to find out the effect of the cooker orientation on its performance, the present analysis is carried out. A method is outlined to find out a reflector performance factor and an orientation factor that depend upon the elevation angle of the sun, the solar surface azimuth angle and the reflector tilt angle. The analysis is applied to a cooker placed at Aden (Yemen). The results indicate that with proper cooker orientation the improvement in the performance of the cooker due to the reflector reached during winter is more than 100% at lower elevation angles and is more than 60% at higher elevation angles. It is concluded that with the help of the analysis the optimum position for any place, for any day of the year and for any specific time of the day can be found.
02/01010 Monthly clearness index values of Turkey by harmonic analysis approach Sahin, A.D. e/ cl. Energy Conversion und Manugrmen~, 2001, 42, (8) 933-940. The clearness index is among the most significant concepts in solar engineering. It gives more information about the atmospheric characteristics of solar stations in addition to the degree of solar energy potential of stations and their surrounding areas. Most often, the clearness index is related to sunshine ratio measurements at a single station without spatial feature searches. In this study, harmonic analysis used to model the monthly clearness index values recorded at nine stations of Turkey with distinct steorological conditions,
02101006 Evaluation of convective heat transfer coefficient in crop drying under open sun drying conditions Anwar, S.I. and Tiwari, G.N. &erg? Coni~ersion rmd Manugemmt, 2001, 42, (5), 627-637. In this paper, an attempt has been made to evaluate the convective heat transfer coefficient operating in crop drying in open sun drying conditions (natural convection). Values of the constants, C and n were obtained by linear regression analysis from experimental data obtained for six crops, namely green chillies, green peas, Kabuli chana, onion, potato and cauliflower. Analysis was also performed for Kabuli charm under natural cooling conditions. Based on the values of C and n convective heat transfer coefficients for these crops were determined. The experimental error in terms of percent uncertainty was also calculated.
02/01007 First order Markov chain model for generating synthetic ‘typical days’ series of global irradiation in order to design photovoltaic stand alone systems Muselli, M. er crl. Energ,r Conwrsion und Mumgemen/, 2001, 42, (6). 675-687. In order to elaborate a generator of ‘typical days’ sequences necessary for sizing photovoltaic (PV) systems, this paper develops a methodology to class daily global solar irradiation based on a first order Markov chain model. The method has been applied for two stations in Corsica (France), and we have limited the number of discriminant parameters computed from the hourly clearness index k/(h). The classification is based on Ward’s method, checked by discriminant analyses. Previous works have shown that the different days could be clustered m three groups with distinct mean values and lower standard deviations. After checking the dependence and the stationary of the Markov’s chain, the presented model allows one to compute the simulated marginal probabilities I’, with a good correlation with the experimental ones. A good correlation has been observed between the simulated and experimental transition probability matrices for both meteorological sites. At least, the sizing of PV systems has shown that the kW h costs, computed from real and simulated systems, present weak relative errors belonging to the range -13.3% to +4.2X, checking
the
global
efficiency
of
the
methodology.
02/01006 Global solar radiation estimation in Algeria Chegaar, M. and Chibani, A. Enrrgy Conversion rmd Mtrncrgetmw~, 2001. 42, (8). 967-973. Two models for estimating monthly average daily global radiation on a horizontal surface have been applied to four different locations.
02/01011 Performance parameters for the design of a solardriven cogeneration system Goktun, S. and Ozkaynak, S. Energy, 2001, 26, (I), 57-64. The power+cooling load-to-heat ratio is defined as the effective utilization factor (EUF) for a cogeneration system as a new performance parameter. The optimum value of overall EUF of a solar cogeneration system is investigated. For optimum operation, primary performance parameters of the system are discussed. The results may provide some theoretical bases for the optimal design of solar cogeneration systems. 02/01012 Simple models of solar radiation data for northwestern part of Turkey Sen, Z. and Tan, E. Energy Conversion cmd Mamgrmen~, 2001, 42, (5) 587-598. An extensive statistical analysis of hourly, daily and monthly measured solar radiation has been performed for a site in the northwestern part of Turkey, leading to statistical models. These models are equally applicable in any part of the world with reassessment of the model parameters. The necessary physical interpretations of the model parameters and their temporal variations are also presented. Once these models are established for the site, then it is possible to evaluate the temporal solar radiation amounts by entering the month of concern in a year. The models appear in the form of parabolic equations with three parameters. Significant relationships between these parameters are also shown. It is possible to estimate monthly average hourly global or diffuse radiation amounts by using these equations. 02101013 Simulation and experimental performance of a solar-heated anaerobic digester Axaopoulos, A. el al. Solar Energy, 2001, 70, (2), 155-164. A mathematical model for simulating an innovative design of a solarheated anaerobic digester has been developed. A swine manure digester having a useful volume of 45 m3 is constructed below ground level and its fix cover is made of flat-plate solar collectors, which are an integral part of the roof structure. The solar collectors are coupled to a heat exchanger immersed in the digester manure. The upper part of the digester, under the tilted cover, forms an airtight enclosure that is used to collect and store the daily produced biogas. The performance of the system is investigated experimentally and the results indicate that the use of solar collectors as a cover reduced the digester thermal losses and positively affects the heat balance of the digester. The system is instrumented and an automatic data logging system is used to provide data for the validation of the system. The proposed model can accurately predict the thermal behaviour of the solar-heated digester compared to the measured data. 02/01014 Solar hydrogen from photovoltaic-electrolyzer systems Bilgen, E. Emvg,v Con~ersron oml Mrrnrrgment. 2001, 42, (9), 1047. 1057. Fuel and Energy
Abstracts
March 2002
123
02/01009 Integration of a desiccant unit in crops solar drying installation: optimization by numerical simulation Hodali, R. and Bougard, J. Energy Conversion and Manugemenf, 2001, 42, (13) 154331558. An adsorption unit of silica gel is designed and integrated in a crops solar drying installation. The installation consists of a direct flat plate forced convective solar dryer connected with a similar solar collector. The daily sorption cycle of the desiccant unit is first investigated and a suitable coupling of the collector, the dryer and the adsorption unit has been selected. The coupling is numerically simulated and applied to the drying of apricots and Morocco under real climatic conditions. The mathematical model assumes non-isotermal processes and employs the basic balances of heat and mass transfer. The developed non-linear partial differential equations were solved by finite difference methods and the physical and operational parameters of the installation were numerically optimized. The integration of the adsorption unit allowed improving the quality of the dried product and permitted a cyclic operation of drying over two days by reducing the drying period from 52 to 44 h.
02/01005 Efficient orientation impacts of box-type solar cooker on the cooker performance Algifri, A.H. and Al-Towaie, H.A. Solar Energr, 2001, 70, (2) 165-170. The addition of a plane reflector to a box-type solar cooker increases the obtained cooker temperature and this depends upon the efficient orientation of the cooker. In order to find out the effect of the cooker orientation on its performance, the present analysis is carried out. A method is outlined to find out a reflector performance factor and an orientation factor that depend upon the elevation angle of the sun, the solar surface azimuth angle and the reflector tilt angle. The analysis is applied to a cooker placed at Aden (Yemen). The results indicate that with proper cooker orientation the improvement in the performance of the cooker due to the reflector reached during winter is more than 100% at lower elevation angles and is more than 60% at higher elevation angles. It is concluded that with the help of the analysis the optimum position for any place, for any day of the year and for any specific time of the day can be found.
02/01010 Monthly clearness index values of Turkey by harmonic analysis approach Sahin, A.D. e/ cl. Energy Conversion und Manugrmen~, 2001, 42, (8) 933-940. The clearness index is among the most significant concepts in solar engineering. It gives more information about the atmospheric characteristics of solar stations in addition to the degree of solar energy potential of stations and their surrounding areas. Most often, the clearness index is related to sunshine ratio measurements at a single station without spatial feature searches. In this study, harmonic analysis used to model the monthly clearness index values recorded at nine stations of Turkey with distinct steorological conditions,
02101006 Evaluation of convective heat transfer coefficient in crop drying under open sun drying conditions Anwar, S.I. and Tiwari, G.N. &erg? Coni~ersion rmd Manugemmt, 2001, 42, (5), 627-637. In this paper, an attempt has been made to evaluate the convective heat transfer coefficient operating in crop drying in open sun drying conditions (natural convection). Values of the constants, C and n were obtained by linear regression analysis from experimental data obtained for six crops, namely green chillies, green peas, Kabuli chana, onion, potato and cauliflower. Analysis was also performed for Kabuli charm under natural cooling conditions. Based on the values of C and n convective heat transfer coefficients for these crops were determined. The experimental error in terms of percent uncertainty was also calculated.
02/01007 First order Markov chain model for generating synthetic ‘typical days’ series of global irradiation in order to design photovoltaic stand alone systems Muselli, M. er crl. Energ,r Conwrsion und Mumgemen/, 2001, 42, (6). 675-687. In order to elaborate a generator of ‘typical days’ sequences necessary for sizing photovoltaic (PV) systems, this paper develops a methodology to class daily global solar irradiation based on a first order Markov chain model. The method has been applied for two stations in Corsica (France), and we have limited the number of discriminant parameters computed from the hourly clearness index k/(h). The classification is based on Ward’s method, checked by discriminant analyses. Previous works have shown that the different days could be clustered m three groups with distinct mean values and lower standard deviations. After checking the dependence and the stationary of the Markov’s chain, the presented model allows one to compute the simulated marginal probabilities I’, with a good correlation with the experimental ones. A good correlation has been observed between the simulated and experimental transition probability matrices for both meteorological sites. At least, the sizing of PV systems has shown that the kW h costs, computed from real and simulated systems, present weak relative errors belonging to the range -13.3% to +4.2X, checking
the
global
efficiency
of
the
methodology.
02/01006 Global solar radiation estimation in Algeria Chegaar, M. and Chibani, A. Enrrgy Conversion rmd Mtrncrgetmw~, 2001. 42, (8). 967-973. Two models for estimating monthly average daily global radiation on a horizontal surface have been applied to four different locations.
02/01011 Performance parameters for the design of a solardriven cogeneration system Goktun, S. and Ozkaynak, S. Energy, 2001, 26, (I), 57-64. The power+cooling load-to-heat ratio is defined as the effective utilization factor (EUF) for a cogeneration system as a new performance parameter. The optimum value of overall EUF of a solar cogeneration system is investigated. For optimum operation, primary performance parameters of the system are discussed. The results may provide some theoretical bases for the optimal design of solar cogeneration systems. 02/01012 Simple models of solar radiation data for northwestern part of Turkey Sen, Z. and Tan, E. Energy Conversion cmd Mamgrmen~, 2001, 42, (5) 587-598. An extensive statistical analysis of hourly, daily and monthly measured solar radiation has been performed for a site in the northwestern part of Turkey, leading to statistical models. These models are equally applicable in any part of the world with reassessment of the model parameters. The necessary physical interpretations of the model parameters and their temporal variations are also presented. Once these models are established for the site, then it is possible to evaluate the temporal solar radiation amounts by entering the month of concern in a year. The models appear in the form of parabolic equations with three parameters. Significant relationships between these parameters are also shown. It is possible to estimate monthly average hourly global or diffuse radiation amounts by using these equations. 02101013 Simulation and experimental performance of a solar-heated anaerobic digester Axaopoulos, A. el al. Solar Energy, 2001, 70, (2), 155-164. A mathematical model for simulating an innovative design of a solarheated anaerobic digester has been developed. A swine manure digester having a useful volume of 45 m3 is constructed below ground level and its fix cover is made of flat-plate solar collectors, which are an integral part of the roof structure. The solar collectors are coupled to a heat exchanger immersed in the digester manure. The upper part of the digester, under the tilted cover, forms an airtight enclosure that is used to collect and store the daily produced biogas. The performance of the system is investigated experimentally and the results indicate that the use of solar collectors as a cover reduced the digester thermal losses and positively affects the heat balance of the digester. The system is instrumented and an automatic data logging system is used to provide data for the validation of the system. The proposed model can accurately predict the thermal behaviour of the solar-heated digester compared to the measured data. 02/01014 Solar hydrogen from photovoltaic-electrolyzer systems Bilgen, E. Emvg,v Con~ersron oml Mrrnrrgment. 2001, 42, (9), 1047. 1057. Fuel and Energy
Abstracts
March 2002
123